This is heavily OEM, vendor and hardware dependent, so.. Your mileage may vary.
And of course this is also heavily brick-friendly if done carelessly, so pay attention to instructions.
AMI
Nuff said then. First of all, you'll need the right AMIBCP version to check which options firmware even has.
Version 4.55 should work with motherboards using Aptio4 (more or less anything released between 2009 and 2015, EFI support should be a clear evidence).
Branch 5.x should instead be for Aptio V stuff (>2015), and 3.x (and older) for the one released <2009.
Obtaining BIOS image should be as easy as checking manufacturer website, but should this not be the case check whatever tool your OEM may have provided, AFUWIN, AFULNX, AFUEFI or the venerable AFUDOS (which still quite prefer MS-DOS to FreeDOS 1.1 tbh)
Once you have program and rom file, you can look into it searching for never-before-seen settings.
If nothing is amiss, then there's nothing else to do here. Otherwise go ahead.
In the rosiest of cases, hacking involved is nothing more than changing ACL for non-default or non-user controls to user.
Shouldn't anything differ from Default, or should this regardless don't work, the second easiest possible scenario is about editing menu panels permissions. You'll need UEFITool, IFR Extractor and a hex editor.
If not even this works, then good luck.
Insyde (aka everything else has gone to the rapture)
http://donovan6000.blogspot.com/2013/06/insyde-bios-modding-advanced-and-power-tabs.html
http://donovan6000.blogspot.com/2013/07/insyde-bios-modding-hidden-settings.html
Editing NVRAM and embedded controller should also be a thing.
But arbitrarily reading and writing bios in software without going all the way through Intel's ME is a mirage (they have secret key combos OOTB though ¯\_(ツ)_/¯)
On all UEFI boards it should be possible to forcefully edit unavailable settings via shell (or linux).
Boldest guys may want to endeavor in laptop GPU overclocking too.